#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int main()
{
	int n, k;
    double sum = 0;
	scanf("%d %d", &n, &k);
	int* a;
	a = (int*)malloc(sizeof(int) * 2*n);
	for (int i = 0; i < 2*n-1; i+=2) {
		scanf("%d %d", &a[i], &a[i + 1]);
	}
	for (int j = 0; j < 2*n-3; j+=2) {
		int q, w, e, r;
		q = a[j];
		w = a[j + 1];
		e = a[j + 2];
		r = a[j + 3];
		double t = (e - q) * (e - q) + (r - w) * (r - w);
	    double x ;
		x = sqrt(t);
		 if (x > 0) {
			 sum += x;
		 }
	}
	double T = k*sum / 50;
	printf("%.9f", T);
	free(a);
	return 0;
}